Stress corrosion cracking of Type 304 stainless steel with mixed Mode I/III loading

The role of hydrogen and crack tip strain rate on the stress corrosion cracking of austenitic stainless steels continues to be an unresolved issue for a number of conditions. Previous studies using Mode I and III loaded samples have been used to suggest that the preference of cracking in Mode I loaded samples supports a hydrogen induced cracking mechanism. However, the lack of crack opening and environmental ingress to the crack tip in Mode III loading leaves some doubt about these conclusions. Stress corrosion cracking tests using a new test sample where the mode mixity between Mode I and III can be varied have been conducted and are reported for sensitized Type 304 SS tested in 0.21 M H3BO3+0.01 M (580 ppm) NaCl. Tests were conducted with samples with cracks at angles of 0, 30 and 45° to the principal loading stress. The results from these tests clearly demonstrated the crack velocity does not decrease with increasing amounts of Mode III loading in contrast to expectations from a hydrogen induced cracking mechanism. The crack velocity showed a slight maximum for samples with crack angles of 30° relative to 0 and 45°. The reason for this maximum is not known but could be the result of increasing crack tip strain rates with increasing Mode III loading.